1. Field of the Invention
The present invention relates to a ball joint used at an oscillating portion of a suspension of an automobile, and particularly to an improvement in a ball joint comprising a ball stud, a ball socket for swingably retaining a ball-shaped head of the ball stud with a bearing interposed therebetween, a retaining ring having a cylindrical portion fitted to a shank of the ball stud and a pair of large and small flanges protruding from axially outer and inner ends of the cylindrical portion, and a boot having first and second annular beads fitted to the retaining ring and the ball socket, the first mounting bead being formed with an inner periphery seal portion and an end face seal portion which are adapted to come close contact with the cylindrical portion and the large flange of the retaining ring, respectively.
2. Description of the Related Art
Such a ball joint is already known, for example, as disclosed in Japanese Patent Application Laid-open No.11-63245.
In the conventional ball joint, the first mounting bead of the boot is clamped by a pair of large and small flanges of the retaining ring, whereby the axial movement thereof is restrained, so that the first mounting bead is prevented from being separated from the retaining ring.
In the conventional ball joint, however, if the ball stud is swung relative to the ball socket in a state in which the boot has been hardened due to the freezing of mud or snow deposited to the boot and the like, the first mounting bead is pushed strongly against the small flange of the retaining ring in a side where a tensile force is applied to the boot. For this reason, there is a possibility that an excessive stress is generated in the first mounting bead, resulting in a deteriorated durability of the first mounting bead.
Accordingly, it is an object of the present invention to provide a ball joint, wherein even when the ball stud and the ball socket are swung relative to each other in the state in which the boot has been hardened due to the freezing of mud or snow deposited to the boot and the like, the generation of an excessive stress in the first mounting bead can be avoided to ensure the durability of the first mounting bead.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a ball joint comprising a ball stud, a ball socket for swingably retaining a ball-shaped head of the ball stud with a bearing interposed therebetween, a retaining ring having a cylindrical portion fitted to a shank of the ball stud and a pair of large and small flanges protruding from axially outer and inner ends of the cylindrical portion, and a boot having first and second annular beads fitted to the retaining ring and the ball socket, the first annular bead being formed with an inner periphery seal portion and an end face seal portion which are adapted to come into close contact with the cylindrical portion and the large flange of the retaining ring, respectively, wherein a clearance is provided between the first annular bead and the small flange for permitting the movement of the first annular bead toward the small flange.
The end face seal portion and the inner periphery seal portion correspond to an end face seal lip 26 and an inner periphery seal lip 27, respectively, in an embodiment of the present invention which will be described hereinafter.
With the first feature, when the boot is in a state in which it has been hardened due to the freezing of mud or snow deposited to an outer peripheral surface of the boot, even if the ball stud and the ball socket are swung relative to each other, the first annular bead is pulled toward the ball-shaped head and moved toward the small flange while sliding within the cylindrical portion of the retaining ring, in a side where the tensile force of the boot is applied. Thus, it is possible to avoid the generation of an excessive stress in the boot to ensure the durability of the boot.
If the movement of the first annular bead toward the small flange were excessive, the separation of the first annular bead from the retaining ring can be inhibited by abutment of the inner end face of the first annular bead against the small flange.
According to a second aspect and feature of the present invention, in addition to the first feature, both of the small flange of the retaining ring and the inner end face of the first annular bead opposed to the small flange are formed into tapered shapes such that they are inclined toward the ball-shaped head in a radially outward direction.
With the second feature, when the first annular bead is moved excessively toward the small flange, whereby the inner end face thereof is put into abutment against the small flange, an abutment shock can be dispersed radially outwards by the mutually abutting tapered faces of the inner end face and the small flange, whereby the damage to the first annular bead due to the abutment shock can be prevented. The formation of the inner end face and the small flange into the tapered shapes as described above ensures that a predetermined clearance can be provided between the inner end face and the small flange without setting the axial dimension of the cylindrical portion of the retaining ring at a specially large value, thereby avoiding an increase in size of the ball joint.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.